For example, it has been known a semiconductor device having a reverse-conducting IGBT (hereinafter referred to as RC-IGBT) structure in which an IGBT and a FWD are formed in one chip, as a switching element to be used to an inverter or the like. (For example, see Patent Literature 1.)
In the semiconductor device, a base layer is disposed in a surface layer portion of a semiconductor substrate forming an n−-type drift layer. The semiconductor substrate has a trench gate structure that penetrates through the base layer. A p-type collector layer and an n-type cathode layer are disposed on a back surface of the semiconductor substrate. N-type emitter regions are disposed in a part of the base layer located above the collector layer. An n-type field stop layer (hereinafter referred to as the FS) is disposed in the drift layer at a position corresponding to a boundary between the collector layer and the emitter layer. Further, an upper electrode is disposed adjacent to a front surface of the semiconductor substrate to be electrically connected to the base layer and the emitter regions, and a lower electrode is disposed adjacent to the back surface of the semiconductor substrate to be electrically connected to the collector layer and the cathode layer.
In such a structure, a region having the collector layer on the back surface of the semiconductor substrate serves as an IGBT region, and a region having the cathode layer on the back surface of the semiconductor serves as a diode region. That is, in the semiconductor device described above, the boundary between the collector layer and the cathode layer corresponds to the boundary between the IGBT region and the diode region.